1. Field of the Invention
The present invention relates to a vehicle guidance system capable of showing a recommendable route between the present position of the vehicle and a destination on a map.
2. Description of the Prior Art
FIG. 1 is a block diagram showing the configuration of a vehicle guidance system disclosed in Japanese Patent Laid-open (Kokai) No. 2-28800. Referring to FIG. 1, the vehicle guidance system comprises a data processing unit which executes control programs for guiding a vehicle, a traffic information receiving unit 2 for receiving traffic information transmitted by a traffic information center through transmitters installed on road signboards, the posts of traffic signals and the like, a compact disk player 3 serving as an external read-only storage device for reading road map data stored on a compact disk, a CRT display (cathode-ray tube display) 4 for displaying pictures represented by signals provided by the data processing unit 1, an operating unit 5 comprising input devices, such as key switches and a light pen, a self-supported position sensor 6. The data processing unit 1 comprises a CPU 11, a ROM 12, a RAM 13 and an I/O interface 14. These components of the data processing unit 1 are interconnected by a bus 15.
In operation for finding an optimum route to the destination, the user specifies the destination with the light pen or the like of the operating unit 5 on a road map represented by road map data read by the compact disk player 3 and displayed on the CRT display 4. Then, the data processing unit 1 decides a recommendable route between the present position and the destination through sequential steps of finding a recommendble route between the present position detected by the self-supported position sensor 6 and the destination, selecting routes meeting predetermined restrictive conditions from among the possible routes, and selecting a recommendable route from among the routes selected in the second step and meeting the predetermined restrictive conditions on the basis of traffic information received by the traffic information receiving unit 2 and predetermined routing conditions. Then, the data processing unit 1 displays the recommendable route on the road map displayed on the CRT display 4.
Inventions relating to such a known vehicle guidance system are disclosed, for example, in Japanese Patent Laid-open (Kokai) Nos. 63-148115, 63-171377, 1-161111 and 2-224200.
The known vehicle guidance system thus constructed is not provided with any means for coping with traffic congestion. If the vehicle is involved in traffic congestion at a place unknown to the passengers and where traffic information is unavailable while traveling by the recommended route, it is impossible to estimate the length of a congested section on the route.